This invention relates generally to fuel supply systems which are employed in connection with internal combustion engines. More particularly, the present invention relates to fuel circuits for fuel supply systems which involve fuel injection.
Generally, the fuel injection system contains a fuel injection pump that delivers a higher flow of fuel than is consumed by the engine at the maximum engine power demand. Conventionally, the excess fuel flow is delivered back to the fuel reservoir. Fuel injection pumps are high pressure pumps that generally generate a large amount of heat. Much of this heat is absorbed by the fuel flowing through the pump. The excess fuel returning to the fuel reservoir carries a portion of this heat.
The absence of high standards of quality control in diesel fuel supplies dictates that an effective fuel filter be incorporated into the fuel supply system for a diesel engine. It is not uncommon for diesel fuel to have significant quantities of abrasive particles and water. Diesel fuel also contains a waxy constituent which precipitates as wax crystals when the fuel temperature drops below a characteristic "cloud point". In cold weather conditions, the precipitating wax crystals can rapidly plug a fuel filter and thereby cut off fuel delivery to the internal combustion engine.
A number of conventional fuel filters perform the dual function of removing particulate material from the diesel fuel and separating water from the fuel. Commonly, such fuel filters employ a disposable filter cartridge which is replaced at pre-established intervals of filter usage. Conventional fuel filters may also include a heater element for warming the fuel before it enters the filter cartridge. Such heating elements require positive control to ensure that the proper amount of heat is applied to the fuel. Some conventional fuel supply systems recirculate a portion of the fuel that has been heated by the fuel injection pump. The heated fuel is recirculated to the inlet of the fuel filter to raise the temperature of the fuel that is entering the fuel filter. Such fuel supply systems have typically employed check valves and flow control devices to control the flow of the recirculated fuel and thereby control the temperature of the fuel that enters the fuel filter. These check valves and flow control valves are generally separate components that require mounting in an already crowded engine compartment. In addition, the piping or tube required to connect the check valves and flow control devices takes up additional engine compartment space and requires additional mounting hardware.